#include <iostream>
using namespace std;
struct TreeNode {
  int val;
  TreeNode* left;
  TreeNode* right;
  TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};
/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
 public:
  TreeNode* invertTree(TreeNode* root) {
    if (root == NULL)
      return root;
    else {
      swap(root->left, root->right);
      invertTree(root->left);
      invertTree(root->right);
      return root;
    }
  }
};